Ventricular shunt having a variable pressure valve

ABSTRACT

Proper cerebral hydraulic conditions may be maintained in the treatment of hydrocephalus by means of a ventricular shunt having a variable operating pressure valve, such that the CSF pressure may be controlled according to the size of the ventricle to correct the imbalance of forces developed by the CSF pressure against the ventricular area. These forces can be sensed in the dural region and utilized to control the operating pressure setting of the valve.

Unite States Patent 1191 [111 3,

Hakim Dec. 9, 1975 [54] VE T I SHUNT HAVING A 2,969,066 1/1961 Holter etal 12s/350 v VARIABLE PRESSURE VALVE 3,109,429 11/1963 Schwartz 128/350V 3,477,438 11/1969 Allen et al 128/349 BV Inventor: Salomon Hakim,Carrera 13, 6, 3,654,932 4/1972 Newkirk 128/350 v Bogota, Colombia [22Filed; June 12, 1974 Primary ExaminerRichard A. Gaudet AssistantExaminer-Henry J. Recla PP 9434 Attorney, Agent, or FirmKenway & .lenneyRelated US. Application Data [62] Division of Ser. No. 280,451, Aug. 14,1972, [57] ABSTRACT Proper cerebral hydraulic conditions may bemainabandoned.

tained in the treatment of hydrocephalus by means of [52] US. Cl.128/350 V; 128/274 a entricular Shunt having a variable operating pres-[51] Int. Cl. A61M 27/00 Sure al e, Such that the CSF pressure may becon- [58] Field of Search 128/350 V, 350 R, 349 BV, trolled according tothe size of the ventricle to correct 128/274; 251/342 the imbalance offorces developed by the CSF pressure against the ventricular area. Theseforces can be [56] Reference Cited sensed in the dural region andutilized to control the UNITED STATES PATENTS operating pressure settingof the valve.

1 Claim, 8 Drawing Figures U.S. Patent Dec.9,1975 Sheet10f2 3,924,635

FIG.

US. Patent Dec. 9, 1975 Sheet 2 of2 3,924,635

FIG. 4

FIG. 5

I'll ,4154% VENTRICULAR SIIUNT HAVING A VARIABLE PRESSURE VALVE This isa division, of application Ser. No. 280,451 filed Aug. 14, 1972 and nowabandoned.

BACKGROUND OF THE INVENTION The treatment of hydrocephalus frequentlyinvolves the provision of a ventricular shunt for draining excesscerebral spinal fluid (CSF) from the ventricle in the brain. The shuntgenerally consists of a cerebral catheter inserted through the braintissue into the ventricle and connected through a one-way valve systemto drain into the jugular vein or another resevoir in the body. Theshunt provides for removal of excess CSF from the ventricle andconsequent reduction in its size. Control over the drainage is providedby the one-way valve, which normally operates at a fixed closingpressure.

Although hydrocephalus is frequently associated with an abnormally highCSF pressure, there are numerous cases where hydrocephalus is associatedwith the CSF at normal pressure, see Ojemann, Robert 6., Normal PressureHydrocephalus, Clinical Neurosurgery, Vol. 18 pp. 337-370, 1971.

An analysis of the hydromechanics involved in normal pressurehydrocephalus syndrome leads to the conclusion that the effective forceexpansion from the ventricles is not dependant on the CSF pressurealone, but is the product of the CSF pressure and ventricular area. Inother words, in the presence of ventricular enlargement a normalpressure is acting. Thus, in normal pressure hydrocephalus the ventricleremains enlarged, because the area subjected to the pressure of the CSFis larger than normal and hence the total force on the brain tissue, theproduct of the pressure times the area, is excessive. (See S. Hakim andR. D. Adams, The special clinical problem of symptomatic hydrocephaluswith normal cerebrospinal fluid pressure: Observations on cerebrospinalfluid hydrodynamics. J. Neural. Sci., Vol. 2 pp. 307327. 1965).

In addition to the forces developed by the CSF pressure, the braintissue is subjected to a counterforce developed by the venous pressurewithin the intraparenchymatous system, within the brain tissue itself.Wheras CSF pressure tends to enlarge the ventricles, the venous pressuretends to reduce their size. These two forces are normally in balance sothat the ventricular size does not increase nor decrease, but remainsconstant through life.

Accordingly, the aim in treating hydrocephalus by shunting procedures isnot merely to arrest the condition, but to restore, as much as possible,normal ventricular size. Once hydrocephalus has developed, thisrestoration is accomplished by reversing the imbalance of the two forcesacting on the brain parenchyma. The CSF pressure must be reduced by anamount proportional to the size of the ventricles to offset the increaseforce developed by virtue of their enlarged area. Then the forcesdeveloped within the venous system can cause the compressed brain tissueto spring back against the lower CSF force, and the venous bed willregain its lost volume and free flow. This way brain metabolism becomesnormal and the tissue recuperates.

In treating hydrocephalus, a reduced CSF pressure is established by ashunt which includes a on'eway valve having an operating pressure equalto the desired CSF pressure. With the shunt in place the CSF pressureremains at a maximum level determined by the implanted valve anddrainage of CSF fluid from the ventricles continues as long as CSFpressure is not less than the operating pressure of the valve. Since thecorrection of normal pressure hydrocephalus requires the implantation ofa valve having a lower than normal operating pressure, e.g. 3040 mm. HO, the CSF pressure remains lower than normal as the ventricle decreasesin size. On the other hand the venous pressure remains normal; as aconsequence the force imbalance is reversed. The venous system forcebecomes greater than the CSF system force because of the progressivelysmaller ventricular area and lowered CSF pressure. Accordingly, once theventricle is again normal size the intraventricular CSF pressure must bebrought back to normal levels. Otherwise there is not enough forcewithin the ventricle to keep the brain normally expanded.

If on the other hand lower than normal CSF. pressure is maintained,overcorrection of hydrocephalus may cause undesirable pathologicalconsequences, such as swelling or engorgement of the veins, cerebraledema, slit ventricles" and microcephaly. In other cases complicationssuch as subdural hygromas, hematomas and overlapping of the skull bonesare known to occur.

The ability to control the CSF pressure with respect to the ventriculararea is important to the proper treatment of hydrocephalus, becauseproper balance within the brain, must eventually be established.

In brief the problem in correcting and maintaining correct normalhydrodynamic balance in the cranial cavity is to maintain theinterventricular CSF at a pressure corresponding to the ventriculararea. When the ventricle attains normal size, the valve provided for theinitial drainage should be replaced with one having a closing pressureequivalent to a normal CSF pressure (125-150) mm. H O.

To date there has been little recognition of the problem of maintainingthe correct balance of CSF pressure, ventricular area and venouspressure within the brain. 7 In an ideal shunt system the valve shouldprovide for initial drainage at a lower than normal pressure andthereafter operate at an operating pressure that maintains the correctintercranial balance.

Accordingly, in one aspect this invention provides a ventricular shuntvalve having means to adjust and vary the valve operating pressure withrespect to ventricular area such that the proper balance of forceswithin the cranium may be maintained.

In another aspect the invention makes use of the fact that the braintissue is itself a viscoelastic solid which transmits the forcedeveloped at the ventricles outwardly to the dura region. This force maybe sensed and utilized to control the operating pressure of theventriculoatrial shunt valve appropriately to maintain proper drainagecondition and balance of forces.

BRIEF DESCRIPTION OF THE INVENTION drainage of CSF from the ventricle ata properly low valve operating pressure (e.g. 45 mm. H O) when the 3force of the CSF is excessive, and to provide for an elevated operatingpressure as the brain tissue relaxes and the ventricular area decreases.

Applicant has discovered that the force on the brain resulting from theCSF pressure exerted over the area of the ventricle is transmittedthrough the brain tissue as a viscoelastic solid and may be sensed inthe subdural space where the brain lies adjacent to the skull. Thisinvention features a sensor adapted to be inserted into the dural regionbetween the brain and the skull, in as sociation with a ventricularvalve having a working pressure that varies inversely with the forceapplied to the sensor.

In the preferred embodiments of the invention, inverse variation of theoperating pressure of the valve is provided by a feedback arrangement,preferable hydraulic, wherein the force applied to the sensor istransmitted to counteract the spring bias which controls the operatingpressure, thus to lower the operating pressure as the force increases.The spring which is biased to hold the valve closed, is unloaded inresponse to the force applied by the brain to the sensor.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The preferredembodiment of this invention is described below with reference to theaccompanying drawings in which:

FIG. 1 is a schematic illustration showing the valve system in itsphysiological enviomment;

FIG. 2 is a longitudinal cross-sectional view of the preferred valvemechanism and sensor of this invention;

FIG. 3 is a longitudinal cross-sectional view illustrating an embodimentfeaturing a resilient slotted tube valve mechanism;

FIG. 4 is a longitudinal cross-sectional view illustrating a valvemechanism featuring a mechanical brain force sensing control element;

FIG. 5 is a plan view showing the implantation of the valve mechanismillustrated in FIG. 4;

FIG. 6 is a longitudinal cross-sectional view, including a partialsagital section, illustrating a resilient slotted tube valve mechanismdirectly operable by brain forces;

FIG. 7 is a top plan view of the embodiment shown in FIG. 6; and

FIG. 8 is a transverse cross-section taken in 88 in FIG. 7.

The implantation of the ventricular shunt in illustrated in FIG. 1. Aventricular catheter 50 inserted through a burr holw 52 in the skull 54and through the brain tissue 58 into the ventricle 56 connects through aone-way drainage valve 60 to a drainage catheter 62 which will normallylead to the right artium, the peritoneal cavity or some other suitablereservoir. The improved shunt valve of this invention is contained inthe valve 60. The force exerted on the brain is sensed by a fluid filledbladder 24 which hydraulically connects by tube 25 to the valve 60mechanism described below. The sensing bladder is inserted also throughthe burr hole, and preferably through the dura] membrain 64 to lieagainst the arachnoidal membrain 66 over one or more convolutions e.g.68. Best response to the forces in the brain require close associationof the sensing bladder with the brain tissue (cortex). The subarachnoidspace surrounding the convolutions is itself subject to CSF pressure,and would tend to give a pressure,

4 rather than a force, response to a sensor output. The object, it willbe noted, is to sense the force exerted by the brain tissue asdistinguished from the pressure of the CSF.

As in general with ventricular shunts the entire drainage assembly isultimately covered and held in place by the scalp (not shown).

The hydraulic servo shunt valve of this invention as embodied in FIG. 2constructed generally as described in applicants US. Pat. No. 3,288,142,and features a housing 10, a valve body 12 formed with a conical valveseat 15 which forms the outlet from an inlet channel 14. A sphericalvalve member 16, held down by a spring 18, rests within the conical seatand maintains the valve closed until the fluid pressure at this inlet issufficient to overcome the bias force of the spring.

The spring 18, is mounted on a base plate 20 which is pivoted to thebody 12 at the end of the-spring away from the valve sphere. Apreloading spring 21 extends from a forward shoulder 19 of the body andpositions the base plate 20 for normal or maximum valve spring bias. Thebase plate 20 lies in spaced relation to a re- -cess portion of thevalve body on which is mounted a valve bladder 22 which is hydraulicallyconnected by tube 25 to the sensing bladder 24. The valve bladder 22 isconstructed to expand when hydraulically loaded to push the base plate20 against the force of the preloading spring 21 and thereby unload thevalve spring by moving it in the direction away from the valve sphere16. The valve spring 18 is thus unstrained such that the force appliedto the sphere is reduced, correspondingly reducing the working pressureof the valve; which is the fluid pressure at the inlet required to openthe valve. When implanted the outward force exerted by the brain isapplied to the sensing bladder 24 situated in the subdural regionbetween the brain and the skull, and is transmitted hydraulically to thevalve bladder 22. Thus when the force exerted by the CSF pressureapplied over the ventricular area is increased, the operating pressureof the valve is reduced, and vice versa. Accordingly as the hydraulicbrain contracts from CSF drainage, the resultant reduction in the brainforce brings about an increased operative pressure effective to maintainproper drainage and a balance of forces.

Both the sensing bladder 24 and the valve bladder 22 are convenientlyconstructed of silicone rubber discs cemented together at their edges bymeans of silicone cement which may be of the RTV type or polymerizableby ionizing radiation. Silicone tubing 25 attached to the discs providesfor hydraulic connection between the bladders. The bladders and tubingare conveniently filled with a radiopaque oil such as ethyl iodophenylundecylate which provides appropriate viscous dampening of the valvemechanism, permits the hydraulic servo connection to be radiologicallyviewed, and is a safe material frequently used in myelography.

It will be understood that the valve mechanism described in FIG. 2 isthe downstream end of the check valve pair described in US. Pat. No.3,288,142, and is mounted in a flexible length of hollowing tubing 11which surrounds the housing 10.

The actual construction is more or less conventional,

with stainless steel being preferred for the housing 10, valve body 12,spring 18, base plate 20 and preloading spring 21. The spherical valvemember 16 is preferably synthetic sapphire. The biasing spring 18 isspot-welded to the base plate 20 and the preloading spring 21 isspot-welded to the transverse shoulder 19. The pivotal mounting of thebase plate to the downstream end of the valve body consists of a pinmember 23 spot-welded to the lower side of the base plate 20, receivedat its ends within sleeves 26, conveniently formed of pieces ofhypodermic needle tubing, spot-welded to the top side of the downstreamend of the valve body 12. The tube passes through an opening 27 in thevalve body 12 and also through the tubing 11 to which it may be sealedby silicone cement.

Implantation of the valve of this invention in a ventriculoatrial shuntsystem follows standard surgical procedures, with the additionalprocedure of inserting the sensing bladder 24 into the subdural region.Most conveniently this is introduced through the burr hole and thenlaterally a short distance away to lie between the brain and the skull.

After the system has been implanted, it may be desirable to makehydraulic adjustments to the servo connection to insure that the valvewill open and close properly in response to variations in the force atthe sensor. This may be accomplished by shimming the sensor with thinpieces of silicone, or by injecting or removing fluid with a hypodermicneedle, preferably through a side branch tube (not shown) which maysubsequently be sealed.

In the emb diment illustrated in FIG. 3 the valve consists in aresilient hollow closed tube 70 formed with a longitudinal slit 72. TheCSF fluid enters the valve tube 70, and under sufficient pressure causesthe slit 72 to open for drainage. The slit is also under the control ofan internal spherical bladder 22a, hydraulically connected to thesensing bladder 24 and expansible under hydraulic pressure to urge theslit to open.

In the embodiment illustrated in FIGS. 4 and 5, the construction isgenerally as described with reference to FIG. 2 with the exception thatthe control mechanism consists of a pin 76 mounted to the underside ofthe base plate 20, passing through a silicone rubber seal 78. The pin 76is adjustably connected, e.g. threaded, to a sensing button 80, adaptedto be placed in contact with the exterior of the brain in the duralregion. The threaded engagement between the pin 76 and the sensingbutton 80 provides for adjustment to the individual patient.

The mounting of this embodiment is illustrated in FIG. 5 and featurestwo burr holes 85 and 86, the former accommodating the catheter 50 andthe latter accommodating the sensing mechanism. The valve mechanism isconveniently attached to the skull by a mounting pin 90 which passesthrough the valve body 12 and terminates in eyes by which the valve canbe fastened to the skull, e.g. by screws 92.

In the embodiment illustrated in FIGS. 6, 7, and 8, the valve mechanismis contained within a resilient chamber 102, e.g. silicone rubber,formed for direct placement in the dural region in contact with thebrain. The catheter 50 leads into the chamber 102 and terminates in aresilient closed tube having a transverse slit 108 on a side wallprotion. The top and bottom of the tube 100 contact opposite top andbottom walls of the chamber 102 and may incorporate small metal discs106. A drainage catheter 104 leads from the chamber 102.

In operation, sufficient CSF pressure will cause the slit 108 to openand provide drainage from the catheter 50 into the chamber 102. Shouldexcessive forces develop, the chamber 102 becomes squeezed and the discs106 compress the tube 100 causing the slit 108 to tend to open. Drainageat a lower CSF pressure is thus provided. As the brain contracts theforce applied by the discs 106 is lessened and an increased CSF pressurebecomes necessary for drainage. Thus proper drainage conditions andbalance of forces may be maintained.

From the foregoing it will be noted that this invention has beendescribed with specific reference to its prefe'rred embodiment, it iscontemplated that numerous modifications and alternatives will readilyoccur to those skilled in the art and familiar with the principlesherein disclosed and that such may principles herein disclosed and thatsuch may be adapted or utilized without departing from the scope of thisinvention.

Having thus disclosed my invention, I claim and desire to secure byLetters Patent:

1. A cerebrovascular shunt valve comprising a resilient valve bodyadapted to be inserted into the dural region, said valve body havingopposed wall portions adapted to bear against the skull and the brainrespectively;

a resilient tube which extends into said valve body between said wallportions and is adapted for connection to a ventricular catheter, theend of the tube being closed within the valve body, there being a slitin the side wall of the tube within said valve body for communicatingCSF from said catheter into said valve body, said slit extending in adirection normal to the direction of the longitudinal axis of the tubeand positioned between said opposed wall portions thereby being orientedwith respect to the wall portions of said valve body to produce openingof said slit when said wall portions are driven against said tube bypressure of the brain against the skull; and

outlet means for venting CSF from said valve body to a location outsideof the skull.

1. A cerebrovascular shunt valve comprising a resilient valve bodyadapted to be inserted into the dural region, said valve body havingopposed wall portions adapted to bear against the skull and the brainrespectively; a resilient tube which extends into said valve bodybetween said wall portions and is adapted for connection to aventricular catheter, the end of the tube being closed within the valvebody, there being a slit in the side wall of the tube within said valvebody for communicating CSF from said catheter into said valve body, saidslit extending in a direction normal to the direction of thelongitudinal axis of the tube and positioned between said opposed wallportions thereby being oriented with respect to the wall portions ofsaid valve body to produce opening of said slit when said wall portionsare driven against said tube by pressure of the brain against the skull;and outlet means for ventinG CSF from said valve body to a locationoutside of the skull.